1. Field of the Invention
The invention relates to a composite and to a process for producing the composite.
2. Description of the Related Art
Thermoplastic fluoropolymers can be processed by common thermoplastic methods, for example casting, blowing extrusion, injection molding, thermoforming, blow molding, etc. They typically possess properties such as low gas permeabilities, media resistance, low flammability, low surface energy and low coefficients of friction. Their end uses therefore range from architectural films through medical equipment to pipes and conduits for chemical apparatus construction, among others. A disadvantage of these fluoropolymers is, however, their low adhesion to chemically different substances, for example minerals such as marble, metals such as steel, or polymers such as polypropylene. This inadequate adhesion can be improved by pretreatment, for example by plasma processes, chemical etching or the use of primers, but this is generally associated with increased costs.
WO 07/079028 describes laminates composed of thermoplastic fluoroelastomers with adhesives based on organosilicone copolymers and MQ resins, which do not require the pretreatment of thermoplastic fluoropolymers. MQ resins are well known in the art and comprise monofunctional “M” siloxy units having the formula R3Si—O— (R3SiO1/2) and quadrifunctional “Q” siloxy units,
(SiO4/2) where R is an organo group. Such resins are more fully described in U.S. published application 2007/0148473, equivalent to WO 07/07928, in paragraphs [0075] to [0079]. A disadvantage of these articles and processes is that one side of the article is permanently tacky, which, especially in the case of film or roll products, for example films finished therewith, has an exceptionally unfavorable effect on the unwind behavior. In other words, the roll of the fluoropolymer finished with the adhesive can be unwound only with extreme difficulty, and even the placing on a surface to be adhesive-bonded is very complicated, specifically in the case of large areas owing to the adhesive character. To avoid this behavior, it is in turn necessary to add a further release liner in a costly and inconvenient manner, which in turn leads to increased costs and also waste.
In addition, the transparency of the PSA layer of organosilicone copolymer is reduced by use of the MQ resins. There was therefore a need for a means of finishing thermoplastic fluoropolymers in a simple manner with an adhesive layer which does not have the disadvantages just mentioned.